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CONTENTS
Introduction
Data and Methods
Results
Discussion
References

Northeast Fisheries Science Center Reference Document 05-03

Description of the 2004 oceanographic conditions on the northeast continental shelf

Maureen H. Taylor, Cristina Bascuñán, and James P. Manning
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods Hole, MA 02543

Web version posted April 12, 2005

Citation: Taylor MH, Bascuñán C, Manning JP. 2005. Description of the 2004 oceanographic conditions on the Northeast Continental Shelf. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 05-03; 92 p.

Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.

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ABSTRACT: A summary of hydrographic observations for 15 surveys on the northeast continental shelf during 2004 is presented.  Distributions of CTD stations, surface and bottom temperature, salinity, and anomalies are portrayed.  The average surface and bottom temperatures and salinities have been calculated in five geographic regions over the northeast continental shelf:  western Gulf of Maine (GOMW), eastern Gulf of Maine (GOME), Georges Bank (GB), northern Middle Atlantic Bight (MABN) and southern Middle Atlantic Bight (MABS).  Time series plots from various shipboard environmental sensors are included if available.

Hydrographic data collected during 2004 were sorted into six 2-month time bins to provide the best spatial coverage used in the averaging method.  A comparison of the computed areal average temperature and salinity data for 2004 with the MARMAP reference values indicate that the majority of the shelf experienced relatively cold bottom temperatures and fresher salinities in all regions during the majority of the observations made during the year.

INTRODUCTION

The Northeast Fisheries Science Center (NEFSC) conducts several different surveys off the northeast continental shelf each year.  Complete coverage of the shelf (Cape Hatteras to the Gulf of Maine) occurs during the spring and fall bottom trawl surveys and during some of the Ecosystem Monitoring cruises.  Station coverage on other cruises throughout the year varies.

Temperature and salinity observations from 15 NEFSC surveys conducted during 2004 are summarized and presented in this report.  Cruise operation summaries are presented for all cruises.  Distribution plots of surface and bottom temperature, salinity, and anomalies are contoured where sufficient data are available.  Areal average temperature and salinity and the corresponding anomalies also are presented for the five different regions on the shelf and for 6 time periods throughout the year.  The data are presented chronologically in atlas form.  Environmental data from the SCS system (Shipboard Computing System) are presented as time series figures for each leg of a cruise.  No attempt has been made here to rigorously analyze the data or discuss in detail individual observations from the cruises.

DATA AND METHODS

All raw Profiler data were processed using the Seabird manufactured software: DATCNV, FILTER, ALIGNCTD, BINAVG, DERIVE, and ASCIIOUT to produce 1 decibar averaged ASCII files.  The data were edited, cleaned, and converted to a standard 80-column ASCII formatted cruise file and were archived in ORACLE tables and in the NEFSC anonymous FTP account (ftp://ftp.wh.whoi.edu/pub/hydro).

Station distributions and horizontal contour plots of the surface and bottom temperature, salinity, and temperature anomaly were prepared for each survey if coverage was sufficient.  In addition, all the hydrographic data were combined and sorted into 2-month time bins.  Areal average temperatures and salinities were then calculated for the six time periods and for the five regions of the northeast continental shelf shown in Figure 1a:  western and eastern Gulf of Maine (GOMW, GOME), Georges Bank (GB), and the northern and southern Middle Atlantic Bight (MABN, MABS).  Station distributions for each time period are shown in Figure 1b.  Anomalies for the temperature and salinity observations were determined relative to reference values, using the method described by Holzwarth and Mountain (1990) as modified by Mountain et al. (2004).   The areal averaging was also done using the method described in Holzwarth and Mountain (1990) as modified by Mountain et al. (2004).  The areal averages and anomalies were plotted against the calendar mid-date of all observations within each of the six time periods.  Areal averages and anomalies were also calculated by cruise and are listed in Table 4 and Table 5.

RESULTS

The NEFSC cruises that are included in this report are listed in Table 1.  A summary of each cruise is described in Appendix A and includes information on the type of cruise, its objectives, dates, the number of hydrographic stations, type(s) of instruments used, salinity calibration value, and notes pertaining to instrument performance.    No salinity correction was applied to the cruise data if the mean salinity offset was less than +/- 0.01 psu.  

Table 2 lists the surface and bottom areal average temperatures and temperature anomalies that were calculated for each of the five regions.  Table 3 lists the surface and bottom areal average salinity and salinity anomalies for the same five regions.  For most cruises, the areal averages and anomalies could not be calculated for all regions due to limited station coverage.  Combining all the hydrographic data from all NEFSC programs and ships provided a better chance of adequate spatial and temporal coverage within the regions of the northeast continental shelf.   In some cases however, a simple average (not an areal weighted mean) was determined for the observations in the region; these values are indicated in Tables 2 - 4 with a flag value of '1'.  The standard deviations are also listed.  SDV1 indicates how well the calculated anomaly represents the true regional average anomaly.  SDV2 is an indicator of how closely the areal average matches the anomaly at any particular location within that region (see Holzwarth and Mountain, 1990 for further explanation of SDV1 and SDV2).

Figure 2 and Figure 3 present the time series of surface and bottom average temperature/salinity and temperature/salinity anomaly for each region.  Cruises having less than 10 observations were not included in the time series figures.  We were not able to resolve small-scale, localized events because of the regional averaging method used in this report.  Station positions and distributions of surface and bottom temperature, salinity, and anomalies for the different cruises are presented in Figures 4 - 55.  Contour distribution figures were not prepared for some of the cruises because of poor station coverage.   In addition, contour levels are not always consistent for a variable within a cruise.  Contour distributions have been routinely produced for the scallop survey although the station coverage for this survey does not provide sufficient spatial coverage to allow one to produce realistic broad-scale hydrographic distributions of the MAB and Georges Bank regions.   Environmental time series plots from shipboard sensors (SCS data) are included in Appendix B.  Further information about this data may be obtained at http://www.wh.whoi.edu/~jmanning/foi/alongtrack.html.

DISCUSSION

The bottom temperature anomaly time series (Figure 2) indicates that the bottom temperatures of the entire northeast continental shelf were colder  (= 1°C) for much of the year.  Similarly, the salinity anomaly pattern displayed in Figure 3 indicates that the shelf region was also fresher than the MARMAP reference annual cycle.  The salinity anomaly time series suggests a pattern of increasing freshness in the Georges Bank and Gulf of Maine regions with the year ending with these regions having salinity values approximately 0.5 fresher than the reference period.  The air temperatures during January 2004 were approximately 6 degrees below average in the northeast region every day for the month (Northeast Regional Climate Center, 2004), and the cold atmosphere likely contributed to the colder bottom temperatures observed on the northeast continental shelf during much of the year.  The fresher surface and bottom salinities suggest an increase in cold, fresh scotian shelf water entering the eastern Gulf of Maine and being advected during the year 'downstream' into the Georges Bank and MAB regions.

REFERENCES

Holzwarth, T.J. and D. Mountain. 1990. Surface and bottom temperature distributions from the Northeast Fisheries Center spring and fall bottom trawl survey program, 1963-1987. Woods Hole, MA: Northeast Fisheries Center. Reference Document 90-03. Available from: Information Services Section, NMFS/Northeast Fisheries Science Center, Woods Hole, MA 02543 

Manning, J.P. (2004).  NEFSC Scientific Computer System (SCS) Alongtrack Data Processing.  http://www.wh.whoi.edu/~jmanning/foi/alongtrack.html (10 Dec 2005).

Mountain, D.G., M.H. Taylor and C. Bascuñán.  2004.  Revised Procedures for Calculating Regional Average Water Properties for Northeast Fisheries Science Center Cruises. Woods Hole, MA:  Northeast Fisheries Center.  Reference Document 04-08.  Available from:  Information Service Section, NMFS/Northeast Fisheries Science Center, Woods Hole, MA 02543.

Northeast Regional Climate Center, Cornell University.  Seasonal Climate Summary Tables. http://met-www.cit.cornell.edu/ (10 January 2005).

Taylor, M. H. and Bascuñán, C. 2000.  CTD Data Collection on Northeast Fisheries Science Center Cruises: Standard Operating Procedures.  Northeast Fisheries Science  Center Reference Doc. 00-11; 28 p.  Available from: National Marine Fisheries Service,  166 Water St., Woods Hole, MA 02543.

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